A scale of 1 to 5 was adopted for assigning effectiveness numbers. 

 As noted above, the effectiveness number attempts to quantify the degree 

 to which each conceptual design fulfills the operating requirements 

 listed in Table 2; the larger the number, the better the system meets 

 the requirement. For the first four requirements, quantitative limits 

 can be established for each of the effectiveness numbers, as shown in 

 Table 3. For the remaining requirements, the effectiveness number 

 represents the judgment of the relative quality of each conceptual 

 design, Table 4 summarizes the conceptual designs, the effectiveness 

 number assigned for each requirement, and the overall effectiveness 

 rating of each system. 



Discussion 



All of the conceptual designs can meet the requirement that the 

 submerged weight be less than 40 kips. However, the multiple-vibratory 

 driver system will be just below this limit and is down-rated compared 

 to the other systems, as shown in Table 4. The weight estimates for 

 the vibratory systems are based on a driver-to-pile weight ratio of 

 3 to 1. This ratio is about average for successful commercial vibratory 

 drivers. 



The required power is estimated to be the least for the jack-in 

 system and the greatest for the vibratory systems. However, the vibra- 

 tory systems have a potentially greater emplacement rate and may permit 

 shorter on-bottom operation times. The lower relative rating of the 

 emplacement rate of the jack-in and screw-in systems reflects their 

 status as "static" emplacement methods. 



The jack-in system is rated much superior to the others in ability 

 to assume and maintain a vertical pile attitude (i.e., level template 

 attitude), because the jacks at each corner can be used to level the 

 template at the beginning and end of the pile-jacking sequence. The 

 attitude of the other systems depends upon how nearly vertical they 

 hang when the piles are released from the template to free-fall the 

 final 3-5 feet. 



The screw-in emplacement method is believed to be the most adaptable 

 to differing soil conditions. Industry experience with this means of 

 emplacing ground anchors for electric utility lines and pipelines has 

 shown that screw piles can be configured to penetrate dense cohesionless 

 and very stiff cohesive soils at the proposed power levels^. The vibra- 

 tory driver systems are relatively inefficient in cohesive soils and 

 would probably penetrate the stiff cohesive soils only with consider- 

 able difficulty. The jack-in system is not expected to operate 

 effectively in cohesionless soils because the point resistance of the 

 driven pile would increase too rapidly with depth for the skin fric- 

 tion on the adjacent piles to provide sufficient reaction force. 



10 



